Green synthesis of NiO and NiO@graphene oxide nanomaterials using leaves: Structural and electrochemical studies.

An eco-friendly synthetic route was developed for the formation of nickel oxide (NiO and NiO) nanoparticles (NPs) by treating Ni(NO).6HO with aqueous/ethanolic extracts of leaves; the same reaction was performed in the presence of graphene oxide (GO) to produce NiO@GO and NiO@GO nanocomposites (NCs), respectively. The NMs were characterized by XRD, FT-IR, SEM, EDX, UV-visible spectroscopy, and TGA-DSC analysis. They were also subjected to electrochemical investigations and photocatalytic degradation of crystal violet (CV) dye. XRD analysis revealed the average crystallite sizes of 8.84-14.07 nm with a face-centered cubic form of NiO NPs and a hexagonal structure of their nanocomposites with GO. FT-IR spectroscopy confirmed the presence of Ni-O vibrations at 443-436 cm. SEM images confirmed the spherical morphology of NiO NPs while NiO@GO NCs contained randomly aggregated, thin, and wrinkled graphene sheets. NiO and NiO have shown particle sizes of 27.7-30.63 nm which were decreased to 19.33-26.39 nm in their respective NiO@GO and NiO@GO NCs. EDX spectra verified the homogeneous distribution of elements (Ni, O, C) on the surface of the particles. The synthesized NCs have shown smaller band gaps (NiO@GO = 3.74 eV; NiO@GO = 3.34 eV) as compared to their respective NPs (NiO = 5.0 eV; NiO = 3.89 eV). TGA/DSC data was used to find the thermal stabilities, glass transition temperatures, and enthalpies. Cyclic voltammetry measurements exhibited distinct oxidation and reduction peaks. NCs exhibited better potential as electrode materials for supercapacitor applications as compared to their respective NPs. NiO@GO exhibited the best electrochemical performance and photocatalytic degradation efficiency of CV dye. After 120 min exposure to sunlight, the degradation coefficient of CV was observed to be 82.93, 86.34, 89.99, 90.27 and 81.65 % in the presence of NiO, NiO, NiO@GO, NiO@GO and GO, respectively.